46 lines
1.2 KiB
C
46 lines
1.2 KiB
C
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#include "poly.h"
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static uint16_t mod3(uint16_t a) {
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uint16_t r;
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int16_t t, c;
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r = (a >> 8) + (a & 0xff); // r mod 255 == a mod 255
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r = (r >> 4) + (r & 0xf); // r' mod 15 == r mod 15
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r = (r >> 2) + (r & 0x3); // r' mod 3 == r mod 3
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r = (r >> 2) + (r & 0x3); // r' mod 3 == r mod 3
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t = r - 3;
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c = t >> 15;
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return (c & r) ^ (~c & t);
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}
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void PQCLEAN_NTRUHRSS701_CLEAN_poly_mod_3_Phi_n(poly *r) {
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int i;
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for (i = 0; i < NTRU_N; i++) {
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r->coeffs[i] = mod3(r->coeffs[i] + 2 * r->coeffs[NTRU_N - 1]);
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}
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}
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void PQCLEAN_NTRUHRSS701_CLEAN_poly_mod_q_Phi_n(poly *r) {
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int i;
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for (i = 0; i < NTRU_N; i++) {
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r->coeffs[i] = r->coeffs[i] - r->coeffs[NTRU_N - 1];
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}
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}
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void PQCLEAN_NTRUHRSS701_CLEAN_poly_Rq_to_S3(poly *r, const poly *a) {
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/* NOTE: Assumes input is in [0,Q-1]^N */
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/* Produces output in {0,1,2}^N */
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int i;
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/* Center coeffs around 3Q: [0, Q-1] -> [3Q - Q/2, 3Q + Q/2) */
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for (i = 0; i < NTRU_N; i++) {
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r->coeffs[i] = ((MODQ(a->coeffs[i]) >> (NTRU_LOGQ - 1)) ^ 3) << NTRU_LOGQ;
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r->coeffs[i] += MODQ(a->coeffs[i]);
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}
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PQCLEAN_NTRUHRSS701_CLEAN_poly_mod_3_Phi_n(r);
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}
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